The introduction of MIMO capabilities in existing WCDMA/HSPA networks is an important step in the evolution of the technology towards higher spectral efficiency and bitrates. With MIMO at least two transmit antennas needs to be used within the same cell. However, the introduction of a second transmit antenna port has a negative influence for legacy user equipment (UE) for which the signals transmitted on the second antenna port will show up as interference, as illustrated in FIG. 1. Ideally, since the second antenna port signals, such as the S-CPICH and the MIMO streams, are transmitted with channelization codes that are orthogonal to the ones used for the legacy users, this interference will be fully orthogonal and therefore completely suppressed. However, the orthogonality of the codes is only guaranteed when the codes are transmitted over non-dispersive channels, which is typically not the case. Even a state of the art MMSE receiver will not be able to fully suppress this interference. Thus the presence of a S-CPICH pilot or MIMO traffic in the cell can have negative consequences for the perceived communication quality for a UE that is demodulating information only from antenna port 1, referred to in the following as a legacy user.
Therefore, there is a need of methods and arrangements for reducing the interference for legacy user equipment in a MIMO capable communication system.